1. Field of the Invention
The present invention relates to a photographing technology, and particularly to the technology of a photographing apparatus for a microscope which is suitable for observing rapid aging of a sample.
2. Description of the Related Art
In the field of physiology, it is required that rapid aging of a sample be captured when a dynamic state of the sample, a reaction caused by an optical or electrical stimulus, or the like is observed using a photographing apparatus for a microscope and when such an image is recorded. In order to meet such a requirement, there is a photographing apparatus with a partial reading function that does not read electric charges, generated from an imager via a photoelectric conversion, from pixels in the entire region of the light receiving surface but reads them from only a portion of the region, so as to achieve a high frame rate. This partial reading function is also called partial scanning, sub array reading, ROI (Region Of Interest) reading, and the like.
As representative imagers, a CMOS (Complementary Metal Oxide Semiconductor) image sensor and CCD (Charge Coupled Device) image sensor have been introduced. Of these imagers, a CMOS image sensor can directly specify and output an electric charge generated by each pixel on a light receiving surface by means of an XY address technique; therefore, partial reading can be easily achieved. Meanwhile, although due to its structure a CCD image sensor cannot randomly access and output an electric charge generated by each pixel on a light receiving surface, substantial partial reading is made possible by devising a method for driving this image sensor.
In regard to a partial reading technique via such a CCD image sensor, some techniques are conventionally proposed.
For example, Japanese Laid-open Patent Publication No. 2004-104561 describes a technology of partial reading by a CCD image sensor, which is performed via high-speed sweeping. In regard to normal reading, when a charge transport corresponding to one horizontal line on an imager is completed, the imager is shifted by one vertical line. In regard to high-speed sweeping, by contrast, when the transport above is completed, line shifting corresponding to a plurality of lines is performed and electric charges corresponding to the plurality of lines are mixed and swept out. In this technology, time spent on reading non-ROI regions is shortened by performing normal reading for a region for which partial reading is performed (e.g. ROI) and by performing high-speed sweeping for the other regions, so that the frame rate is improved.
As another example, Japanese Laid-open Patent Publication No. 2004-304652 proposes a technology of reading an image signal from a CCD image sensor so as to improve a frame rate. In this technology, before completing the output of electric charges corresponding to one frame of a certain image, electric charges are output for the subsequent frame, so that reading is performed on the basis of the cycle of a vertical synchronization signal which needs fewer horizontal scan lines than when normal reading is performed.
As another example, Japanese Laid-open Patent Publication No. 2008-35391 discloses a technology for enhancing the output rate of image data from a CCD image sensor so as to improve the frame rate. In this technology, before all of the electric charges corresponding to one horizontal line on the CCD image sensor are transported, the CCD image sensor is vertically shifted, so that electric charges of unnecessary regions are mixed.
Assume, for example, that a user observes a dynamic state of a sample in detail and that in order to record the image of this sample, this user photographs the image of this sample at a frame rate desired by the user. In this situation, if the desired frame rate is higher than the frame rate for the all-pixel reading operation (i.e., a reading operation performed over pixels of the entire region of the light receiving surface of an imager), this desired frame rate can be achieved using a partial reading function. However, the relationship between the partial reading region and the frame rate depends on the configuration and operation of the apparatus, such as the kind of imager and its driving method. Therefore, the user cannot find out if it is possible to perform photographing at the frame rate above without actually performing photographing by means of a partial reading function.
Assume, for example, a photographing apparatus for a microscope which has, as an imager, a CCD image sensor whose pixel number is 1360 [pixels] (horizontal)×1024 [pixels] (vertical) and whose transfer cycle for one horizontal line is 64 [μsec]. If 32 [bit] of RAW images (raw data images) are output from the photographing apparatus when the exposure time is 10 [msec], the maximum frame rate will be 15 [fps] since about 66 [msec] are needed to read one image frame.
Also assume that the partial region of, for example, 1360 [pixels] (horizontal)×300 [pixels] (vertical) in the RAW image is output via the partial reading based on high-speed sweeping (7 lines are assumed to be swept away). In this situation (the details will be described later), about 26 [msec] will be needed to read one image frame and the maximum frame rate will be 38 [fps].
Also assume that, for example, USB 2.0 (transfer rate: about 480 Mbps) of the USB (Universal Serial Bus) standard, which is one of the serial bus standards, is used when image data photographed by the photographing apparatus for a microscope is transferred to a PC. In this situation, the frame rate of an RAW image is limited to 10 [fps] at most due to the transfer rate of a transfer path; and if the partial reading described above is used, the frame rate of an image is limited to 36 [fps] at most.
As described above, some photographing parameters indicative of various conditions at the time of photographing an image may have a mutual relationship, such as a relationship between a frame rate and the size of a partial reading region.
Therefore, when, for example, a certain parameter is fixed depending on a user's request, the settable range for other photographing parameters may be constrained due to the fixing. As described above, there may be a restraint condition between photographing parameters having a mutual relationship.
As described above, this restraint condition depends on the apparatus configuration, such as the kind of an imager used, a method used for reading accumulated electric charges from the imager, and the transfer rate of an image data transfer path; therefore, it is difficult for the user to estimate the combination of settable photographing parameters before photographing is performed. Thus, until the setting of a desired photographing condition or photographing condition closest to the desired condition is found for a photographing apparatus, the user needs to repeatedly adjust a plurality of photographing parameters and repeatedly perform photographing (i.e., test photographing). It is very troublesome to set a photographing condition.